The amount of final wort collected does not effect your boil time. The 60 minute boil is primarily about extracting bitterness from your first hop addition with some possible secondary effects such as caramelizing some of the sugars in your wort (a buddy of mine once let a batch boil for 2 hrs, don't ask why, but made an amazing brew by accident that was darker and sweeter than originally planned).
Also note that the volume of wort at the end of an hour is a lot less than you started with, so don't start with a gallon if you want to do a one gallon batch. You will lose a significant (10-20%) amount of volume through evaporation. There are some good online calculators that will help you estimate the amount of liquid you will lose over the boil, but also keep records for your self so you can learn how your specific brew set up behaves.
If you are doing small batches and have not already bought it you should check out the Brooklyn Brewshop's book. The specialize in small batch brewing and recipes.
